.box{
  color:red
}
a{
  /* display: block;
  height: 50px; */
}
.header{
  height: 50px;
  position: fixed;
  width: 100%;
  top:0;
  left: 0;
  display: flex;
  align-items: center;
  color:#fff
}
.header span{

}
.content{
  position: fixed;
  top:50px;
  bottom:50px;
  left: 0;
  right:0
}
.footer{
  height: 50px;
  position: fixed;
  width: 100%;
  bottom:0;
  left: 0;
}